Oral exposure to thiacloprid-based pesticide (Calypso SC480) causes physical poisoning symptoms and impairs the cognitive abilities of bumble bees

Abstract Background: Pesticides are identified as one of the major reasons for the global pollinator decline. However, the sublethal effects of pesticide residue levels found in pollen and nectar on pollinators have been studied little. The aim of our research was to study whether oral exposure to the thiacloprid levels found in pollen and nectar affect the learning and long-term memory of bumble bees. We tested the effects of two exposure levels of thiacloprid-based pesticide (Calypso SC480) on buff-tailed bumble bee (Bombus terrestris) in laboratory utilizing a learning performance and memory tasks designed to be difficult enough to reveal large variations across the individuals. Results: The lower exposure level of the thiacloprid-based pesticide impaired the bees’ learning performance but not long-term memory compared to the untreated controls. The higher exposure level caused severe acute symptoms, due to which we were not able to test the learning and memory. Conclusions: Our results show that oral exposure to a thiacloprid-based pesticide, calculated based on residue levels found in pollen and nectar, not only causes sublethal effects but also acute lethal effects on bumble bees. Our study underlines an urgent demand for better understanding of pesticide residues in the environment, and of the effects of those residue levels on pollinators. These findings fill the gap in the existing knowledge and help the scientific community and policymakers to enhance the sustainable use of pesticides

Field-realistic acute exposure to glyphosate-based herbicide impairs fine-color discrimination in bumblebees

Abstract Pollinator decline is a grave challenge worldwide. One of the main culprits for this decline is the widespread use of, and pollinators’ chronic exposure to, agrochemicals. Here, we examined the effect of a field-realistic dose of the world’s most commonly used pesticide, glyphosate-based herbicide (GBH), on bumblebee cognition. We experimentally tested bumblebee (Bombus terrestris) color and scent discrimination using acute GBH exposure, approximating a field-realistic dose from a day’s foraging in a patch recently sprayed with GBH. In a 10-color discrimination experiment with five learning bouts, GBH treated bumblebees’ learning rate fell to zero by third learning bout, whereas the control bees increased their performance in the last two bouts. In the memory test, the GBH treated bumblebees performed to near chance level, indicating that they had lost everything they had learned during the learning bouts, while the control bees were performing close to the level in their last learning bout. However, GBH did not affect bees’ learning in a 2-color or 10-odor discrimination experiment, which suggests that the impact is limited to fine color learning and does not necessarily generalize to less specific tasks or other modalities. These results indicate that the widely used pesticide damages bumblebees’ fine-color discrimination, which is essential to the pollinator’s individual success and to colony fitness in complex foraging environments. Hence, our study suggests that acute sublethal exposure to GBH poses a greater threat to pollination-based ecosystem services than previously thought, and that tests for learning and memory should be integrated into pesticide risk assessment